Luminescence shock avoidance in display devices

ABSTRACT

A luminescence shock avoidance algorithm selectively limits the brightness level of a display device when the display device is activated in a dark environment to prevent the temporary vision impairment that can occur when a display device is activated in a dark environment. The algorithm receives the state of the display (e.g. on or in standby mode), and can optionally receive an ambient lighting value from an ambient light sensor and a user-selectable manual brightness adjustment setting to determine whether luminescence shock avoidance should even be triggered, and if it is triggered, how much should the brightness level of the display be limited.

This application is a continuation of U.S. patent application Ser. No.13/304,176, filed Nov. 23, 2011, which is a continuation of U.S. patentapplication Ser. No. 11/800,293, filed May 4, 2007, now U.S. Pat. No.8,068,125, issued Nov. 29, 2011, which claims priority to U.S.Provisional Patent Application 60/878,755, filed on Jan. 5, 2007, eachof which is hereby incorporated by reference herein in its entirety.This application claims the benefit of and claims priority to U.S.patent application Ser. No. 13/304,176, filed Nov. 23, 2011, U.S. patentapplication Ser. No. 11/800,293, filed May 4, 2007, now U.S. Pat. No.8,068,125, issued Nov. 29, 2011, and U.S. Provisional Patent Application60/878,755, filed on Jan. 5, 2007.

FIELD OF THE INVENTION

This invention relates to display devices, and more particularly, toavoiding luminescence shock (temporary vision impairment) when a displaydevice is activated in a dark environment.

BACKGROUND

Many types of input devices are presently available for performingoperations in a computing system, such as buttons or keys, mice,trackballs, touch panels, joysticks, touch screens and the like. Touchscreens, in particular, are becoming increasingly popular because oftheir ease and versatility of operation as well as their decliningprice. Touch screens can include a touch sensor panel, which can be aclear panel with a touch-sensitive surface. The touch sensor panel canbe positioned in front of a display screen so that the touch-sensitivesurface covers the viewable area of the display screen. Touch screenscan allow a user to make selections and move a cursor by simply touchingthe display screen via a finger or stylus. In general, the touch screencan recognize the touch and position of the touch on the display screen,and the computing system can interpret the touch and thereafter performan action based on the touch event.

Because touch screens can reduce or eliminate the need for physicalkeypads or buttons, the touch screens themselves can often be madelarger in comparison to the overall size of the device. These largertouch screens have enabled even small devices such as personal digitalassistants (PDAs), mobile telephones, digital audio/video players, andthe like to provide a wider variety of content than previously possible,including video, graphics, Internet access, photos, and the like. Theconvenience of today's handheld portable devices combined with theirever-increasing multi-media functionality has made such devicesseemingly ubiquitous, with users carrying them everywhere, in purses orclipped to belts. To a dedicated user, these personal devices can be asindispensable as a wallet. To that end, users may place these personaldevices within arms reach wherever they go, including vehicles, movietheaters, and the like.

Because personal devices tend to have small batteries, power savings iscritical. A large display illuminated to full brightness will exhaust abattery in no time, and thus power saving functions such as sleep modesare common in personal devices. For example, the display of a mobiletelephone may be dimmed or go dark altogether until a call is received,or the screen of a PDA may go blank until the user activates a functionor a communication such as an e-mail or text message is received.However, if one of these personal devices is in a sleep mode in a darkenvironment and the display is suddenly illuminated due to a receivedcall or other communication, a nearby user who happens to be looking atthe device or is instinctively drawn to looking at the display when itilluminates can suffer temporary vision impairment. Because the user'spupils have opened up in the dark environment, the sudden flash of lightcan cause short-term blindness or at least impaired vision. Thistemporary impaired vision can range from a mere annoyance to alife-threatening situation if the user is driving a motor vehicle.

SUMMARY

A luminescence shock avoidance algorithm can be employed to selectivelylimit the brightness level of a display device when the display deviceis activated in a dark environment to prevent the temporary visionimpairment that can occur when a display device is activated in a darkenvironment. The algorithm receives the state of the display (e.g. on orin standby mode), and can optionally receive an ambient lighting valuefrom an ambient light sensor and a user-selectable manual brightnessadjustment setting to determine whether luminescence shock avoidanceshould even be triggered, and if it is triggered, how much should thebrightness level of the display be limited.

When a display device is in a standby, sleep or powered-down mode tosave battery power, the display is at a zero brightness level. When thedisplay is automatically activated, such as when a telephone call isreceived, the display can turn on to a brightness level determined bythe ambient light level detected by the ambient light sensor. If thedevice is in a car being driven at night, for example, then when a callor other triggering activity is detected, the display brightness levelmay instantly jump from zero to some predetermined level. Because theuser's eyes are likely to be already adjusted to the darkness of thecar, the sudden change in display brightness level from can causeluminescence shock and temporary vision impairment, which can bedangerous to the operator of the car, especially if the driver takes aglance at the newly illuminated display.

To avoid luminescence shock, if the display device is off and a call orother triggering activity is detected, the ambient light sensor willturn on and detect a certain ambient light level. In one embodiment, ifthe detected ambient light level is greater than or equal to a thresholdvalue, then the display device will turn on at a brightness levelaccording to the current display brightness setting. In other words, ifthe ambient light level is greater than or equal to threshold value, thedisplay will turn on from a zero brightness level to the level definedby the appropriate brightness function as determined by the currentdisplay brightness setting. Because the threshold value is chosen suchthat no luminescence shock is expected for ambient light levels abovethe threshold value, no adjustment is made to the display brightnesslevel when the display turns on.

However, if the detected ambient light level is below the thresholdvalue, luminescence shock may occur, so the display device will turn onfrom a zero brightness level to an initially reduced brightness level ascompared to what would normally be expected if the brightness functionappropriate for the current display brightness level was followed. Inother words, the display will initially turn on to a brightness levelless than the appropriate brightness function as determined by thecurrent display brightness setting. This dimmer than usual brightnesslevel is intended to avoid luminescence shock. After some short timeperiod has passed, giving the user's eyes time to adjust, the brightnesslevel can be gradually or instantly increased to the level determined bythe appropriate brightness function, which should be closer to ideal forsufficient visibility at the current ambient light level.

In other embodiments, a threshold is not used, and therefore regardlessof the detected ambient light level, the display will initially turn onto a brightness level less than the appropriate brightness function asdetermined by the current display brightness setting. Optionally, asabove, after some short time period has passed, the brightness level canbe gradually or instantly increased to the level determined by theappropriate brightness function.

If the display device is already on and a call or other triggeringactivity is detected, there will be no change to the display brightness,regardless of the current light level. In other words, the luminescenceshock avoidance algorithm can be employed only when the display deviceis initially off.

The reduced brightness value may be implemented in a number of differentways. If the detected ambient light level is below a threshold, thereduced display brightness value may be a fixed value, regardless of thecurrent display brightness settings. After some short time period haspassed, the brightness level can be gradually or instantly increased tothe level determined by the brightness function appropriate for thecurrent display brightness settings. Alternatively, the reduced displaybrightness value can be a fixed value that is dependent on the currentdisplay brightness settings. In another embodiment, the reduced displaybrightness value is dependent only on the detected ambient light level,regardless of the current display brightness settings. In still otherembodiments, the reduced display brightness value is dependent both onthe detected ambient light level and the current display brightnesssettings.

Even in embodiments without an ambient light sensor, and therefore nodetected ambient light level, luminescence shock can be avoided. When atelephone call or other triggering activity is detected, the display mayinitially come on with a reduced brightness value as compared to normallevels. After some short time period has passed, the brightness levelcan be gradually or instantly increased to normal levels.

In other embodiments, the wavelength of light from the display can beshifted to further reduce luminescence shock. If ambient light levelsbelow a certain threshold are detected when a telephone call or otheractivity is detected and the display is turned on, the color of thedisplay can be temporarily gamma-shifted into the red region, eitheralone or in combination with reduced display brightness levels asdescribed above. By gamma-shifting the display towards red light, thebrightness of the display will tend to cause the user's pupils toconstrict less, so that when the user looks up again at a dark road, forexample, the user's vision impairment is reduced. If gamma-shifting isapplied in combination with reduced display brightness levels, thedisplay brightness levels may not need to be reduced as much.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary computing system including a displaydevice operable in accordance with a luminescence shock avoidancealgorithm according to one embodiment of this invention.

FIG. 2 a illustrates exemplary brightness functions of ambient light (inlux (one lumen per square meter)) vs. display device brightness orluminance (in nits (one candela per square meter)) for an exemplarydisplay device according to one embodiment of this invention.

FIG. 2 b illustrates a luminescence shock avoidance algorithm wherein ifthe detected ambient light level is below a threshold, the reduceddisplay brightness value may be a fixed value regardless of the currentdisplay brightness settings according to one embodiment of thisinvention.

FIG. 2 c illustrates a luminescence shock avoidance algorithm wherein ifthe detected ambient light level is below a threshold, the reduceddisplay brightness value is a fixed value that is dependent on thecurrent display brightness settings according to one embodiment of thisinvention.

FIG. 2 d illustrates a luminescence shock avoidance algorithm wherein ifthe detected ambient light level is below a threshold, the reduceddisplay brightness value is dependent only on the detected ambient lightlevel, regardless of the current display brightness settings accordingto one embodiment of this invention.

FIG. 2 e illustrates a luminescence shock avoidance algorithm wherein ifthe detected ambient light level is below a threshold, the reduceddisplay brightness value is dependent both on the detected ambient lightlevel and the current display brightness settings according to oneembodiment of this invention.

FIG. 2 f illustrates a luminescence shock avoidance algorithm in whichno ambient light level is detected and the display device initiallyturns on at a reduced brightness level before ramping up to normallevels according to one embodiment of this invention.

FIG. 3 is a plot of wavelength vs. pupil sensitivity, showing that thepupils are more sensitive to blue/green light as compared to red lightto illustrate the purpose of gamma-shifting according to one embodimentof this invention.

FIG. 4 is a more detailed view of the host processor, ambient lightsensor and display device shown in FIG. 1 according to one embodiment ofthis invention.

FIG. 5 a illustrates an exemplary mobile telephone that can includeluminescence shock avoidance algorithms according to one embodiments ofthis invention.

FIG. 5 b illustrates an exemplary digital audio player that can includeluminescence shock avoidance algorithms according to one embodiments ofthis invention.

DETAILED DESCRIPTION

In the following description of preferred embodiments, reference is madeto the accompanying drawings which form a part hereof, and in which itis shown by way of illustration specific embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the preferred embodiments of the presentinvention.

A luminescence shock avoidance algorithm can be employed to selectivelylimit the brightness level of a display device when the display deviceis activated in a dark environment to prevent the temporary visionimpairment that can occur when a display device is activated in a darkenvironment. The algorithm receives the state of the display (e.g. on orin standby mode), and can optionally receive an ambient lighting valuefrom an ambient light sensor and a user-selectable manual brightnessadjustment setting to determine whether luminescence shock avoidanceshould even be triggered, and if it is triggered, how much should thebrightness level of the display be limited.

Although some embodiments of this invention may be described herein interms of mobile telephones, it should be understood that otherembodiments of this invention may not be so limited, but can begenerally applicable to any display device that is capable ofautomatically waking up from a sleep mode and illuminating the displayto a certain level.

FIG. 1 illustrates exemplary computing system 100 operable with touchscreen 142 formed from sensor panel 124 and display device 140 that maybe used in conjunction with embodiments of this invention. However, itshould be understood that the system of FIG. 1 is merely illustrative ofa number of different touch screen systems that can be used withembodiments of this invention.

Sensor panel 124 can include a capacitive touch sensor panel capable ofdetecting touch or hovering within the near-field detection capabilitiesof the capacitive touch sensors, or a proximity sensor panel capable ofdetecting hovering outside the near field detection capabilities of thecapacitive touch sensors, or a combination of both. Examples of acapacitive touch sensor panel and a proximity sensor panel are describedin Applicant's co-pending U.S. application Ser. No. 11/649,998 entitled“Proximity and Multi-Touch Sensor Detection and Demodulation,” filed onJan. 3, 2007, the contents of which are incorporated by referenceherein.

Sensor panel 124 can be connected to other components in computingsystem 100 through connectors integrally formed on the sensor panel, orusing flex circuits. Computing system 100 can include one or more panelprocessors 102 and peripherals 104, and panel subsystem 106. The one ormore processors 102 can include, for example, ARM968 processors or otherprocessors with similar functionality and capabilities. However, inother embodiments, the panel processor functionality can be implementedinstead by dedicated logic such as a state machine. Peripherals 104 caninclude, but are not limited to, random access memory (RAM) or othertypes of memory or storage, watchdog timers and the like.

Panel subsystem 106 can include, but is not limited to, one or moreanalog channels 108, channel scan logic 110 and driver logic 114.Channel scan logic 110 can access RAM 112, autonomously read data fromthe analog channels and provide control for the analog channels. Thiscontrol can include multiplexing columns of sensor panel 124 to analogchannels 108. In addition, channel scan logic 110 can control the driverlogic and stimulation signals being selectively applied to rows ofsensor panel 124. In some embodiments, panel subsystem 106, panelprocessor 102 and peripherals 104 can be integrated into a singleapplication specific integrated circuit (ASIC).

Driver logic 114 can provide multiple panel subsystem outputs 116 andcan present a proprietary interface that drives high voltage driver 118.High voltage driver 118 can provide level shifting from a low voltagelevel (e.g. complementary metal oxide semiconductor (CMOS) levels) to ahigher voltage level, providing a better signal-to-noise (S/N) ratio fornoise reduction purposes. The high voltage driver outputs can be sent todecoder 120, which can selectively connect one or more high voltagedriver outputs to one or more panel row inputs 122 through a proprietaryinterface and enable the use of fewer high voltage driver circuits inthe high voltage driver 118. Each panel row input 122 can drive one ormore rows in sensor panel 124. In some embodiments, high voltage driver118 and decoder 120 can be integrated into a single ASIC. However, inother embodiments high voltage driver 118 and decoder 120 can beintegrated into driver logic 114, and, in still other embodiments, highvoltage driver 118 and decoder 120 can be eliminated entirely.

Computing system 100 can also include host processor 128 for receivingoutputs from panel processor 102 and performing actions based on theoutputs that can include, but are not limited to, moving an object suchas a cursor or pointer, scrolling or panning, adjusting controlsettings, opening a file or document, viewing a menu, making aselection, executing instructions, operating a peripheral deviceconnected to the host device, answering a telephone call, placing atelephone call, terminating a telephone call, changing the volume oraudio settings, storing information related to telephone communicationssuch as addresses, frequently dialed numbers, received calls, missedcalls, logging onto a computer or a computer network, permittingauthorized individuals access to restricted areas of the computer orcomputer network, loading a user profile associated with a user'spreferred arrangement of the computer desktop, permitting access to webcontent, launching a particular program, encrypting or decoding amessage, and/or the like.

Host processor 128 can also perform additional functions that may not berelated to panel processing, and can be coupled to program storage 132and display device 130 such as a liquid crystal display (LCD) forproviding a user interface (UI) to a user of the device. For example, aluminescence shock avoidance algorithm according to embodiments of thisinvention can be implemented in software or firmware and executed byhost processor 128 to selectively limit the brightness level of adisplay device when the display device is activated in a darkenvironment to prevent the temporary vision impairment that can occurwhen display device 130 is activated in a dark environment.

In some embodiments of this invention, an ambient light sensor 144 mayprovide a signal or change in state corresponding to the amount ofambient light present. Ambient light sensor 144 can be a photodiode(e.g. a fast pin diode) 146 or any other device (e.g. a phototransistoror other sensing device) known in the art whose current changes as afunction of received ambient light, and can include both an infrared(IR) sensor and a visible light sensor.

FIG. 2 a illustrates exemplary brightness functions of ambient light (inlux (one lumen per square meter)) vs. display device brightness orluminance (in nits (one candela per square meter)) for an exemplarydisplay device according to embodiments of this invention. Thebrightness functions in FIG. 2 a indicate that, for a given ambientlight level (the x-axis), the display device will be set to a particularbrightness level (the y-axis). FIG. 2 a demonstrates that as the ambientlight decreases, less light is needed from the display to maintainsufficient visibility, and as the ambient light increases, more light isneeded from the display to maintain sufficient visibility. In FIG. 2 a,lines 200, 202, 204, 206 and 208 represent a sampling of brightnessfunctions (or various modified brightness functions) of ambient lightvs. display device brightness that can be selected by a user using amanual display brightness control setting, although it should be notedthat the brightness functions need not be largely linear, but can benon-linear and can even include discrete steps. The brightness functionsmay be mathematical expressions computed by a processor, or look-uptables stored in memory. In the example of FIG. 2 a, line 200 can be thedefault (neutral) display brightness function, but if the user desires alower display brightness, the control setting can be adjusted down,either in continuous or discrete steps, until an absolute minimumdisplay brightness function 202 is reached. Note that in the example ofFIG. 2 a, when function 202 hits a minimum ambient light level 214, itdoes not drop below a minimum display brightness level 210, and thus thedisplay will always be illuminated to some degree, even in absolutedarkness. However, it should be understood that minimum levels 210 and214 are not required.

Conversely, if the user desires a higher display brightness, the controlsetting can be adjusted up, either in continuous or discrete steps,passing through brightness functions 204 and 206, until an absolutemaximum display brightness function 208 is reached. Note that in theexample of FIG. 2 a, function 208 is maintained at maximum displaybrightness level 212. At this setting, there is essentially no longerany sensitivity to ambient light, as the display brightness setting isconstant, regardless of the ambient light level. It also be understoodthat in other embodiments, there may be no manual display brightnesscontrol, and only a single brightness function (e.g. default function200) may be employed.

FIG. 2 a also illustrates that when the display device is in a standby,sleep or powered-down mode to save battery power, the display is at azero brightness level 216. When the display is automatically activated,such as when a telephone call is received, the display will turn on tothe brightness level determined by the ambient light level detected bythe ambient light sensor. For example, if the device was in a brightlylit room when a call is received, the display brightness level may jumpfrom point 218 to point 220. Because the user's eyes are likely to bealready adjusted to the lighting in the room, the sudden change indisplay brightness level from point 218 to point 220 should not causeany luminescence shock. However, if the device is in a car being drivenat night, for example, when a call is received, the display brightnesslevel may jump from point 222 to point 224. Although the displaybrightness level of point 224 is far less than point 220, neverthelessbecause the user's eyes are likely to be already adjusted to thedarkness of the car, the sudden change in display brightness level frompoint 222 to point 224 can cause luminescence shock and temporary visionimpairment, which can be dangerous to the operator of the car.

To avoid luminescence shock, an algorithm may be applied as follows. Ifthe display device is off and a call or other triggering activity isdetected, the ambient light sensor will turn on and detect a certainambient light level. In one embodiment, if the detected ambient lightlevel is greater than or equal to a luminescence shock threshold value226, then the display device will turn on at a brightness levelaccording to the current display brightness setting. In other words, ifthe ambient light level is greater than or equal to threshold value 226,the display will turn on from a zero brightness level to the leveldefined by the appropriate brightness function as determined by thecurrent display brightness setting (e.g. from point 218 to point 220).Threshold value 226 can be determined empirically and then used as afixed value in the algorithm, or it can be user programmable. Becausethreshold value 226 is chosen such that no luminescence shock isexpected for ambient light levels above the threshold value, noadjustment is made to the display brightness level when the displayturns on.

However, if the detected ambient light level is below threshold value226, luminescence shock may occur, so the display device will turn onfrom a zero brightness level to an initially reduced brightness level ascompared to what would normally be expected if the brightness functionappropriate for the current display brightness level was followed. Inother words, the display will initially turn on to a brightness levelless than the appropriate brightness function as determined by thecurrent display brightness setting (e.g. from point 222 to point 228,which is less than point 224). This dimmer than usual brightness levelis intended to avoid luminescence shock. After some short time periodhas passed (e.g. five seconds), giving the user's eyes time to adjust,the brightness level can be gradually or instantly increased to thelevel determined by the appropriate brightness function (see arrow 230),which should be closer to ideal for sufficient visibility at the currentambient light level.

In other embodiments, threshold 226 is not used, and thereforeregardless of the detected ambient light level, the display willinitially turn on to a brightness level less than the appropriatebrightness function as determined by the current display brightnesssetting. Optionally, as above, after some short time period has passed,the brightness level can be gradually or instantly increased to thelevel determined by the appropriate brightness function.

If the display device is already on and a call or other triggeringactivity is detected, there will be no change to the display brightness,regardless of the current light level. In other words, the luminescenceshock avoidance algorithm can be employed only when the display deviceis initially off.

The reduced brightness value may be implemented in a number of differentways. FIG. 2 b illustrates one embodiment of this invention wherein ifthe detected ambient light level is below threshold 226, the reduceddisplay brightness value may be a fixed value 240, regardless of thecurrent display brightness settings. After some short time period haspassed, the brightness level can be gradually or instantly increased tothe level determined by the brightness function appropriate for thecurrent display brightness settings. In the example of FIG. 2 b, twobrightness functions 200 and 204 are shown representing two differentpossible current display brightness settings. If the current displaybrightness settings correspond to brightness function 200, then thedisplay device turns on to a reduced brightness level 240 (see arrows232), and then after some time has passed, the display device returns tothe brightness levels determined by brightness function 200 (see arrows234). Even if the current display brightness settings correspond tobrightness function 204, the display device turns on to the same reducedbrightness level 240 (see arrows 236), and then after some time haspassed, the display device returns to the brightness levels determinedby brightness function 204 (see arrows 238).

FIG. 2 c illustrates one embodiment of this invention wherein if thedetected ambient light level is below threshold 226, the reduced displaybrightness value is a fixed value that is dependent on the currentdisplay brightness settings. After some short time period has passed,the brightness level can be gradually or instantly increased to thelevel determined by the brightness function appropriate for the currentdisplay brightness settings. In the example of FIG. 2 c, two brightnessfunctions 200 and 204 are shown representing two different possiblecurrent display brightness settings. If the current display brightnesssettings correspond to brightness function 200, then the display deviceturns on to a reduced brightness level 240 associated with brightnessfunction 200 (see arrows 232), and then after some time has passed, thedisplay device returns to the brightness levels determined by brightnessfunction 200 (see arrows 234). If the current display brightnesssettings correspond to brightness function 204, the display device turnson to a higher reduced brightness level 246 associated with brightnessfunction 204 (see arrows 242), and then after some time has passed, thedisplay device returns to the brightness levels determined by brightnessfunction 204 (see arrows 244).

As the example embodiment of FIG. 2 c illustrates, the fixed values 240and 246 can depend on the current display brightness settings. Forexample, the higher the current display brightness settings, the higherthe fixed value. At the lowest possible current display brightnesssettings, the fixed value can be the minimum display brightness value210 (see FIG. 2 a).

FIG. 2 d illustrates one embodiment of this invention wherein if thedetected ambient light level is below threshold 226, the reduced displaybrightness value is dependent only on the detected ambient light level,regardless of the current display brightness settings. After some shorttime period has passed, the brightness level can be gradually orinstantly increased to the level determined by the brightness functionappropriate for the current display brightness settings. In the exampleof FIG. 2 d, two brightness functions 200 and 204 are shown representingtwo different possible current display brightness settings. If thecurrent display brightness settings correspond to brightness function200, then the display device turns on to a reduced brightness level asdetermined by the detected ambient light level and reduced brightnessfunction 248 (see arrows 250). Note that although reduced brightnessfunction 248 is shown in FIG. 2 d as a piecewise linear function, anytype of function could be used, as long as it represents a reducedbrightness level. The reduced brightness function may be a mathematicalexpression computed by a processor, or may be a look-up table stored inmemory. After some time has passed, the display device returns to thebrightness levels determined by brightness function 200 (see arrows252). Even if the current display brightness settings correspond tobrightness function 204, the display device turns on to the same reducedbrightness level as determined by the detected ambient light level andreduced brightness function 248 (see arrows 254), and then after sometime has passed, the display device returns to the brightness levelsdetermined by brightness function 204 (see arrows 256).

FIG. 2 e illustrates one embodiment of this invention wherein if thedetected ambient light level is below threshold 226, the reduced displaybrightness value is dependent both on the detected ambient light leveland the current display brightness settings. After some short timeperiod has passed, the brightness level can be gradually or instantlyincreased to the level determined by the brightness function appropriatefor the current display brightness settings. In the example of FIG. 2 e,two brightness functions 200 and 204 are shown representing twodifferent possible current display brightness settings. If the currentdisplay brightness settings correspond to brightness function 200, thenthe display device turns on to a reduced brightness level as determinedby the detected ambient light level and reduced brightness function 248associated with brightness function 200 (see arrows 250). After sometime has passed, the display device returns to the brightness levelsdetermined by brightness function 200 (see arrows 252). If the currentdisplay brightness settings correspond to brightness function 204, thedisplay device turns on to a reduced brightness level as determined bythe detected ambient light level and reduced brightness function 254associated with brightness function 204 (see arrows 256), and then aftersome time has passed, the display device returns to the brightnesslevels determined by brightness function 204 (see arrows 258).

Even in embodiments without an ambient light sensor, and therefore nodetected ambient light level, luminescence shock can be avoided. FIG. 2f illustrates one embodiment of this invention in which when the displaydevice is on, it remains at a constant level 260, regardless of theambient light level. In some embodiments, this constant level 260 can beadjusted up or down as indicated by arrows 262 using a manual displaybrightness control. When a telephone call or other triggering activityis detected, the display may initially come on with a reduced brightnessvalue 264 as compared to line 260 (see arrows 266). After some shorttime period has passed, the brightness level can be gradually orinstantly increased to the level determined by brightness level 260 (seearrows 268).

In some embodiments of this invention, the wavelength of light from thedisplay can be shifted to further reduce luminescence shock. FIG. 3 is aplot of wavelength vs. pupil sensitivity, showing that the pupils aremore sensitive to blue/green light (i.e. the pupils tend to constrictmore) as compared to red light. Thus, if ambient light levels below acertain threshold are detected when a telephone call or other activityis detected and the display is turned on, the color of the display canbe temporarily gamma-shifted into the red region, either alone or incombination with reduced display brightness levels as described above.By gamma-shifting the display towards red light (see arrow 300), thebrightness of the display will tend to cause the user's pupils toconstrict less, so that when the user looks up again at a dark road, forexample, the user's vision impairment is reduced. If gamma-shifting isapplied in combination with reduced display brightness levels, thedisplay brightness levels may not need to be reduced as much.

FIG. 4 is a more detailed view of the host processor, ambient lightsensor and display device shown in FIG. 1. In FIG. 4, host processor 400receives information on detected ambient light levels from ambient lightsensor 402 through an interface which can include and I.sup.2C digitalserial interface 404. Host processor 400 can execute luminescence shocksoftware or firmware 406 and control the brightness of display device408 using control signals 410. In addition, gamma-shift logic 412, whichcan be a color lookup table, can perform the gamma-shifting describedabove to alter the RGB inputs to display device 408 and shift thedisplay to the red spectrum as described above.

FIG. 5 a illustrates an exemplary mobile telephone 536 having sensorpanel 524 and display device 530 and a processor that can include theluminescence shock avoidance algorithms as described above according toembodiments of this invention. FIG. 5 b illustrates an exemplary digitalaudio/video player 538 having sensor panel 524 and display device 530and a processor that can include luminescence shock avoidance algorithmsas described above according to embodiments of this invention. Themobile telephone and digital audio/video player of FIGS. 5 a and 5 b canadvantageously benefit from the luminescence shock avoidance algorithmsbecause they can limit the amount of temporary vision impairment thatcan occur when a previously dark display device is illuminated in a darkenvironment, which can be hazardous in certain situations such as whenthe user is driving a car at night.

Although the present invention has been fully described in connectionwith embodiments thereof with reference to the accompanying drawings, itis to be noted that various changes and modifications will becomeapparent to those skilled in the art. Such changes and modifications areto be understood as being included within the scope of the presentinvention as defined by the appended claims.

What is claimed is:
 1. A method, comprising: activating a displaydevice, wherein activating the display device comprises: with a sensor,detecting a current ambient light level at the display device; and afterdetecting the current ambient light level, increasing a brightness ofthe display device from a zero brightness level.
 2. The method definedin claim 1 further comprising detecting a triggering activity, whereinactivating the display device comprises activating the display device inresponse to detection of the triggering activity.
 3. The method definedin claim 1 wherein increasing the brightness of the display device fromthe zero brightness level comprises: increasing the brightness of thedisplay device from the zero brightness level to a first brightnesslevel when the current ambient light level is below a threshold; andincreasing the brightness of the display device from the zero brightnesslevel to a second brightness level when the current ambient light levelmeets or exceeds the threshold.
 4. The method defined in claim 3 whereinthe second brightness level is greater than the first brightness level.5. The method defined in claim 3 further comprising: when the currentambient light level is below the threshold and a predetermined timeperiod after the display device is activated, increasing the brightnessof the display device to a third brightness level.
 6. The method definedin claim 3 further comprising: receiving user input that adjusts thelevel of the threshold.
 7. An electronic device, comprising: a display;an ambient light sensor; circuitry coupled to the display and to theambient light sensor, wherein the circuitry, prior to activating thedisplay, determines a current ambient light level at the electronicdevice using the ambient light sensor and then activates the display byincreasing the brightness of the display from a zero brightness level.8. The electronic device defined in claim 7 wherein the electronicdevice comprises a mobile telephone and wherein the circuitry activatesthe display in response to a triggering event.
 9. The electronic devicedefined in claim 7 further comprising: a user input device, wherein theelectronic device comprises a mobile telephone and wherein the circuitryactivates the display in response to user input received through theuser input device.
 10. The electronic device defined in claim 7 whereinthe display comprises a touch screen display.
 11. The electronic devicedefined in claim 7 wherein the circuitry activates the display byincreasing the brightness level from the zero brightness level to afirst brightness level whenever the determined current ambient lightlevel is below a threshold and by increasing the brightness level fromthe zero brightness level to a second brightness level whenever thedetermined current ambient light level meets or exceeds the threshold.12. The electronic device defined in claim 7 wherein the circuitryactivates the display by increasing the brightness level from the zerobrightness level to a first brightness level whenever the determinedcurrent ambient light level is below a threshold and by increasing thebrightness level from the zero brightness level to a second brightnesslevel whenever the determined current ambient light level meets orexceeds the threshold and wherein the second brightness level is greaterthan the first brightness level.
 13. The electronic device defined inclaim 12 further comprising: a user input device operable to receiveuser input, wherein the circuitry is operable to adjust the level of thethreshold in response to the user input.
 14. A method, comprising:detecting a triggering activity; with a sensor, detecting a currentambient light level at a display device when the triggering activity isdetected; after detecting the current ambient light level, activatingthe display device.
 15. The method defined in claim 14 whereinactivating the display device comprises: adjusting a brightness of thedisplay device from a zero brightness level to a first brightness levelwhen the current ambient light level is below a threshold.
 16. Themethod defined in claim 14 wherein activating the display devicecomprises: adjusting the brightness of the display device from the zerobrightness level to a second brightness level when the current ambientlight level meets or exceeds a threshold.
 17. The method defined inclaim 14 wherein activating the display device comprises: adjusting abrightness of the display device from a zero brightness level to a firstbrightness level when the current ambient light level is below athreshold; and adjusting the brightness of the display device from thezero brightness level to a second brightness level when the currentambient light level meets or exceeds the threshold.
 18. The methoddefined in claim 14 wherein the sensor and the display device are partof a mobile telephone and wherein detecting the triggering activitycomprises detecting an incoming call to the mobile telephone.
 19. Themethod defined in claim 14 wherein the sensor and the display device arepart of a mobile telephone, wherein the display device comprises a touchscreen, and wherein detecting the triggering activity comprisesdetecting an incoming call to the mobile telephone.